We are investigating the developmental program in highly differentiated cells, specialized for production of one or only a few specific cell proteins. The systems currently under study are primarily the zymogen cells of the silkmoth galea and the silkmoth follicular cells, which produce a proteinaceous eggshell (chorion). We are attempting to analyze differentiation in these cells quantitatively, by measuring rates of specific protein synthesis during development and analyzing the rates in terms of possible controls at several levels of information flow (gene multiplicity, transcription rates, messenger stability, and translation efficiency).